In the “Shortcut icon settings” section, uncheck the “Use the default shortcut icon” checkbox.
If you’ve already uploaded the graphic to your server, you can type in its path directly in the “Path to custom icon” box. Otherwise, click the Browse button, find the graphic you want to use on your computer, then scroll to the bottom of the screen and click “Save configuration”. (PNG and GIF graphics are best, as some versions of Internet Explorer don’t recognize JPG shortcut icons.)
Don’t immediately see a change? Try doing a “power refresh” in your browser to throw away the old version in your browser’s cache.